Toward Precision Non-Covalent Synthesis:A Study Of Controllable Supramolecular Polymerization In Solution And On Substrate

Although controllable covalent polymerization was introduced in the late 1950s and has undergone broad development,its supramolecular counterpart emerged only recently.Precision synthesis of polymers with a specific structure and the accurate molecular weight,which used to be a challenge for covalent polymers,is the current challenge for supramolecular polymers.Hence,there was a crucial requirement for controllable supramolecular polymerization.Nevertheless,the low energy barrier during a supramolecular polymerization process caused intense competition between the nucleation and elongation processes.For this reason,some reported methods realized the controllable supramolecular polymerization by increasing the activation barrier between the monomers and polymers based on a series of specific molecular systems.From the kinetics concept,a series of controllable supramolecular polymerization methods were proposed in this paper by precisely controlling the instant concentration during the supramolecular polymerization process.The main contents of this paper are shown as follows:(1).The photo-cleavage induced supramolecular polymerization method was proposed in the first part.HTPmono and HTPpre were designed and synthesized as the active monomer and the precursor,respectively.HTPpre can release the HTPmono during UV irradiation,further inducing supramolecular polymerization in solution.In this way,we have successfully prepared the fiber-like supramolecular polymers in solution.(2).The photo-cleavage induced surface assisted supramolecular polymerization method was proposed in this part.Based on the coordination between HTPmono and copper,we could use a copper substrate to assist the polymerization process.After dropping the solution of HTPpre on the substrate and irradiating it with UV light,a film filled with fiber-like supramolecular polymers was prepared on the substrate.Furthermore,the spatially controlled supramolecular polymerization could be realized with the help of photolithography method.(3).Herein,we developed a surface-initiated living supramolecular polymerization method by further studying the photo-cleavage induced surface assisted supramolecular polymerization.When we initiate the supramolecular polymerization under low UV intensity,the instant concentration of HTPmono could be maintained at a low value,further inducing the surface-assisted nucleation and making it dominant in the primary stage.Meanwhile,the random nucleation of monomers in solution is restained in this condition.In this way,the supramolecular polymerization proceeded uni-directionally from the copper substrate,and a film filled with homeotropicly aligned supramolecular polymers was prepared on the substrate.Furthermore,we also found that the unidirectional polymerization showed the properties of a living polymerization process,and the kinetics could be modulated by UV intensity and the initial precursor concentration.(4).The chemical energy-assisted controllable supramolecular polymerization in complex environments was realized in this part.We utilize EDC as a chemical fuel to drive the supramolecular polymerization of the amorphously aggregated POR-COOH.POR-COOH will react with EDC to generate the intermediate POR-COOEDC first,which was wellsolvated by solvent molecules.During the following hydrolysis process,POR-COOH molecules were released into the system and thus allowed the polymerization of POR-COOH into 2D nano-sheets.This chemical energy-assisted supramolecular polymerization process could be performed not only in a mild condition with high spatial accuracy but also with high selectivity in complex environments.